The present invention relates to a process for determining quality parameters of a transmission link for digital data streams having a cellular structure, in which each cell has a useful field. This useful field can be freely occupied with data such as, a test signal to be transmitted on the transmission link and to be evaluated upon receipt.
Besides physical transmission lines, transmission links for digital data streams include other components, such as switching equipment, standardized terminals, terminal adapters, as well as terminal equipment (for example, telephones or fax units). In digital communication systems, digital data streams are transmitted at a high speed in an organized form over the transmission links. To evaluate a digital communication system, knowing quality parameters of this type of transmission link is important. Quality criteria, may include, for example, whether portions of the data stream have been lost on the transmission link, what transit time the data has required on the transmission link, whether the sequence of the data was retained, and whether single binary-coded data (bits) were transmitted incorrectly. From communications technology, testing transmission links by injecting a test signal on the input side and by evaluating the test signal after it has been transmitted through the transmission link is known.
To accomplish this, U.S. Pat. No. 4,441,192 discloses a process in which a test signal having a pronounced, peak autocorrelation function is applied to a transmission link on the input side. A compensation circuit is arranged on the output side, downstream from the transmission link to be analyzed. After being appropriately adjusted, this compensation circuit is used to compensate distortions of or disturbances in data signals to be transmitted. Those distortions or disturbances result from transmission characteristics peculiar to the transmission links. In the known process, to adjust the compensation circuit; the impulse response of the transmission link to be analyzed is determined from the cross-correlation of the test signal and the output signal. In this manner, the downstream compensation circuit can be optimally adjusted, even given transmission links having unknown or time-variant transmission characteristics, so that a substantially undistorted data signal is received on the output side.
In principle, the test signal can preferably be let-in in empty areas of a digital data stream to be transmitted under field conditions. However, one must be able to reliably recognize the measuring signal that has been let into the digital data stream.
The test signal can preferably be placed in empty areas of a digital data stream to be transmitted under field conditions. However, the ability to reliably recognize the test signal that has been placed into the digital data stream necessary.
The present invention seeks to provide a process for generating and evaluating a test signal for determining the aforementioned quality criteria and which is reliably recognizable as a test signal.